+1 adding more coins will be better if it is done not by users request but it should be because the casino want to expand the service and try to get more players.
Of course duelbits may do a survey to know which coins is the most used coin in gambling industry or do a pool to know which coins to add.
No need to add many more altcoins, 1-2 more coins is more than enough.
I saw this recently in some other casinos that there are players that ask them to add more altcoins that will help them save fees. I agree about them having a poll or survey to know which is really liked and most used by their players. It could be from this thread or on-site or with their other social platforms. If they'll do, probably they'll be adding the one that has a huge market cap and considered to be one of the top coins. But we shall see if they will consider it.